In these demos, an Expression can be assigned a constant or variable value and can then be used in any formula or plot in the demo. The example used here is called "a", and it represents the magnitude of a vertical stretch of the graph. Try changing its value. You can change it to any number or to any expression involving c, the only variable used in this demo.

Variables in these demos, like intervals, are given minimum and maximum values. Instead of having resolution, however, variables have "steps". If you started a variable at its minimum value, the amount of times you would have to press the ">" button to get to the maximum value would be equal to the number of steps for the variable.

Just as the ">" button increases the variable value by one step, the "<" button decreases the value by one step.

To see an animation in which the variable value keeps increasing or keeps decreasing until it reaches its upper or lower bound, use the ">>" or "<<" button.

In this example, the variable c represents the altitude of the green plane in the 3D Graph window.